1. Field of the Invention
The present invention relates to a stencil mask for limiting an irradiation area of charged particles on a surface of a substrate to a predetermined shape. The charged particles may be ionized atoms, electrons, etc. The stencil mask is suitable for manufacturing a semiconductor device that works as a switching element, light emitting element, light detecting element. The stencil mask is also suitable for manufacturing a micromachine.
2. Description of the Related Art
In the process of manufacturing the semiconductor device, a process is widely used wherein a local area on a surface of a semiconductor substrate is irradiated with the charged particles, and an area apart from this local area is not irradiated with the charged particles. The local area where the charged particles are irradiated is termed an irradiation area in the present specification. The charged particles are introduced into a surface layer of the semiconductor substrate at the irradiation area. The introduced ionized atoms generally work as impurities.
A pattern of the area where the charged particles are introduced into the semiconductor substrate can be controlled by a masking film that prohibits penetration of the charged particles. Generally, the following method is performed for this type of process: a masking film is formed on the entire surface of the semiconductor substrate, penetrating holes are formed in the masking film, and the surface of the semiconductor substrate that is exposed from the masking film is irradiated with the charged particles. This method requires a step of forming the masking film on the surface of the semiconductor substrate, a step of forming the penetrating holes in the masking film, and a step of removing the masking film, etc. This method therefore has the problem that many steps are required for manufacturing the semiconductor device. Stencil masks have been developed in order to solve this problem.
Stencil mask is a masking member in which a penetrating hole has already been formed. In a method of utilizing a stencil mask, the stencil mask is disposed above the semiconductor substrate. The charged particles are irradiated toward the surface of the semiconductor substrate through the penetrating hole in the stencil mask. The stencil mask limits the irradiation area of the charged particles to be substantially equal to the pattern of the penetrating hole. The stencil mask can be used repeatedly for a plurality of semiconductor substrates. The method of utilizing the stencil mask does not require the step of forming the masking film on the surface of the semiconductor substrate, the step of forming the penetrating hole in the masking film, nor the step of removing the masking film. The method of utilizing the stencil mask can therefore considerably reduce the number of steps required for manufacturing the semiconductor device.
The stencil mask comprises a flat plate-shaped member in which the penetrating hole is formed. The penetrating hole has a shape that substantially corresponds to the irradiation area of the charged particles. The penetrating hole is usually formed by etching the flat plate-shaped member using the RIE (Reactive Ion Etching) method or the like. Since there are limits as to the value of the aspect ratio (the value when the depth of the penetrating hole is divided by the width of the penetrating hole) in the currently available etching processes, a thin flat plate-shaped member must be used for forming the penetrating hole whose width is narrow, or for forming a pair of penetrating holes which are separated with a thin wall.
Various types of patterns of the irradiation area are required to be formed on the surface of the semiconductor substrate. Therefore, the penetrating hole or holes of the stencil mask must also be formed in various shapes. As a result, the problem can arise that forming the penetrating hole or holes causes deformation of the plate-shaped member to easily occur near side walls defining the penetrating hole or holes. Techniques for preventing the deformation of the plate-shaped member are required.
Further, there is a case that the pattern of the irradiation area has a looping shape. In this case, the penetrating hole must also have the looping shape. However, when the penetrating hole is in the looping shape, the part of the flat plate-shaped member surrounded by the looping hole becomes separated from the part of the flat plate-shaped member surrounding the penetrating hole. Techniques for preventing this separation are also required.
In order to deal with these problems, a technique was taught in Japanese Patent Application Publication No. 2002-280290, in which beam members are formed within the penetrating hole of the stencil mask. The beam members pass across the penetrating hole, thus connecting one part of the flat plate-shaped member, which had been divided by the penetrating hole, with the other part of the flat plate-shaped member. The beam members strengthen the stencil mask near the side walls defining the penetrating hole, and can prevent the deformation of this part. Further, in the case where the penetrating hole has a looping shape, the beam members connect the part of the flat plate-shaped member surrounded by the looping hole and the part of the flat plate-shaped member surrounding the penetrating hole, thus preventing the inner side of the flat plate-shaped member (island portion) separated from the outer side of the flat plate-shaped member.